The present invention relates to the field of sound producing prosthetic devices for use by laryngectomized patients.
Many devices have been suggested for providing speech capability to laryngectomized patients. One approach involves the provision of a mechanical or electromechanical device to create pitches or tones which are modulated to produce speech. In Richard L. Goode's review entitled "Artificial Laryngeal Devices In Post-Laryngectomy Rehabilitation", which appeared in The Laryngoscope (pages 677-689, 1974), two basic types of artificial larynges, transcervical and transoral larynges, are disclosed. Transcervical larynges are electronic, hand-held, battery-powered, vibrating devices that are placed on the neck to produce voice. While transcervical devices have experienced considerable commercial success, they must be hand held on the neck whle speaking, produce an "electronic" type of speech, leak unwanted sound from the neck, need battery changes, and require a place on the neck that will allow efficient transfer of sound vibrations. Transoral laryngeal devices are electronic or pneumatic devices in which the sound enters the mouth through a tube. While such units produce a loud sound and may be used in early post-operative stages by patients with thick neck tissue who cannot use transcervical devices, transoral devices are noticeable in use, require placement in the mouth, and are prone to saliva blockages. Additionally, transoral devices may result in articulation which is disturbed by the placement of the tube near the tongue and lips, this results in speech which is less intelligible than that produced by transcervical devices.
The desirability of including all of the operative components of an artificial larynx on an intraoral prothesis has long been recognized. See for example U.S. Pat. No. 2,862,209, Col. 1, lines 61-64. Unfortunately, the art has heretofore failed to disclose any complete intraoral device.
One early attempt at an "intraoral" device is the "Tait larynx". In 1974 Goode, supra. described the Tait larynx, "no longer manufactured", as comprising an intraoral earphone attached to a patient's denture or dental retainer, an external power source, external oscillator and external on-off switch. In the Tait device a wire was passed from the intraoral earphone to these external components. While the sound produced by the Tait device is at least comparable to that produced by other transoral larynges, the presence of a wire coming out of the user's mouth makes the Tait device unacceptable to most laryngectomees. For a disclosure of a similar transoral device see U.S. Pat. No. 2,862,209.
Pichler eliminated any need for transoral wiring by suggesting that a wireless induction system could be used to transmit sound from a pocket oscillator driven primary coil worn around the neck to an intraoral secondary coil associated with an intraoral earphone. However, Pichler's device has apparently never been placed on the market. See Goode, supra.
In an attempt to improve upon the Pichler device, Goode suggests that a miniature pulse generator capable of being mounted on a denture or dental retainer can be used to drive a small, waterproof, low impedance, modified insert earphone. Power is provided to the pulse generator by a handheld, external radio frequency generator operating at 100 kHz and using a 15-volt rechargeable battery pack, carried in the pocket, with a battery drain of 780 mW. When the transmitter is held to the cheek, the transmitter coil lies about 1.5 cm from a miniature, tuned receiving coil in the denture.
A wireless electro-larynx consisting of a receiver/speaker concealed in an ordinary denture or prosthesis, and an external transmitter worn under the patient's clothing has been suggested by Zwitman et al. See "Development and Testing of an Intraoral Electrolarynx for Laryngectomy Patients", Zwitman et al, Journal Of Speech And Hearing Disorders, XLIII, 263-269 (May, 1978). In the Zwitman et al device, a 1 millimeter thick receiver is housed in the center of the denture and surrounded by a receiving coil which is used to pick up an incoming differentiated transmitter-generated pulse which is then amplified. This amplified signal is used to change the state of a bistable multivibrator circuit, which then activates an astable multivibrator. This astable multivibrator then begins to oscillate at a repetition rate (fundamental frequency) of 70 Hz to produce an audible buzz. Current is permitted to pass through the receiver for only 0.3 msec periods, which are long enough to facilitate the generation of intelligible speech, while conserving battery life. A plastic tube is attached to the speaker of the Zwitman et al device which extends medially and slightly upward past the mid-line of the palate to a point just short of the opposite side of the dental prosthesis. This tube is intended to transmit sounds to the posterior region of the oral cavity to provide maximum resonance, and to prevent the tongue from occluding the speaker aperture. Two rechargeable batteries are used to power the receiver/speaker for up to five continuous hours. Since the standby current drain is low, Zwitman et al reported that intermittent use of the unit permits it to function for an entire day before recharging is necessary.
In "A Modified Intraoral Electro-larynx", McRae et al, Archives of Otolaryngology 105: 360-361, 1979, and in "The Design of a Wireless-Controlled Intraoral Electro-larynx", Knorr et al, Journal of Bioengineering 1: 165-171, 1977, other designs of intraoral electro-larynges are disclosed.
More recently, in work conducted by Mr. Kenneth Stern, a self-contained, intra-oral artificial larynx has been suggested, and Stern's described circuitry breadboarded. This circuit generates a squarewave of 125 Hz which is used as a clock for a five stage binary counter. Outputs of the counter are logically interconnected through exclusive-or's, amplified, and used to energize a speaker to produce a buzz. By using bi-lateral switches, most of the circuitry is not powered in order to extend battery life.
Stern has suggested the desirability of providing a tongue operated switch for power control, and of providing a speaker housed in the mouth which produces varied output frequencies which simulate changes of pitch; however Stern has failed to provide designs for these components.
As seen from the above, the desirability of providing a completely self-contained, intraoral artificial larynx has long been recognized. Nonetheless, there is a long felt need for a simple, intraoral, tongue-controlled larynx which may function without recharging over extended periods of time, and which facilitates the generation of clearly audible speech.